Generally, an air compressor includes an air suction pipe, an impeller rotated at high speed about a rotary shaft, a diffuser (diffusive flow passage) connected to an outlet of the impeller, and a discharge pipe through which compressed air ejected from the diffuser is discharged to the outside.
The suction pipe is provided with an inlet guide vane (IGV) which opens or closes a flow passage to regulate air flow into the impeller. The impeller accelerates and compresses air suctioned through the inlet guide vane, and the diffuser reduces noise and the flow speed of the air discharged at high pressure and high speed from the impeller while increasing blowing efficiency.
In FIGS. 1 and 2, a conventional inlet guide vane assembly includes an air suction pipe which guides a flow of air at atmospheric pressure towards the compressor, and variable vanes which protrude into the air suction pipe such that the angle of the vanes can be regulated by external force to allow variable regulation of a flow rate of suctioned air.
Such a conventional inlet guide vane assembly can regulate compression capacity of the compressor by regulating inflow amount, but reduces the discharge pressure and design flow rate of the compressor. Further, in the conventional inlet guide vane assembly, an unsteady flow is created due to generation of a large vortex downstream of the inlet guide vane (IGV), such that abnormal load is applied to impeller blades. Further, the vortex generated at the inlet guide vane causes fatigue of the compressor impeller, which reduces durability of the compressor, and unsteadiness and pressure loss of air flow passing through the inlet guide vane cause a reduction in discharge flow rate, even when the inlet guide vane is completely open. Further, a signification reduction in discharge flow rate occurs due to an increase of pressure loss resulting from opening and closing of the inlet guide vane, and unsteadiness of the flow is severe, thereby increasing load applied to the impeller. Therefore, there is a need for an air compressor which overcomes such problems of the related art.